The purpose of this work is to investigate physiological and pathological aspects of the renin-angiotensin system, with emphasis on the regulation of aldosterone secretion by the zona glomerulosa of the adrenal gland. Specific topics include the characterization and regulation of angiotensin II (AII) receptors, the actions of AII and other regulators of aidosterone secretion, the production and metabolism of AII, and the use of enzyme-dispersed adrenal cells for analysis of the relations between AII receptors and aldosterone production. These studies have shown that vascular and adrenal receptors from AII undergo reciprocal regulation during changes in sodium balance, in keeping with the concomitant changes in vascular and adrenal sensitivity for AII. The effects of AII on aldosterone secretion were found to be selectively inhibited by somatostatin, for which high-affinity receptors were identified and characterized in the rat zona glomerulosa. The role of calcium in the steroidogenic action of AII was further analyzed by ionophore studies which indicated that changes in cytosolic calcium lead to stimulation of aldosterone production by glomerulosa cells. Other studies were initiated on the dopaminergic control of aldosterone secretion, and the characteristics of AII receptors in the human adrenal gland.